Shock excited oscillator circuit



G. R. GAMERTSFELDER 2,671,173 SHOCK EXCITED OSCILLATOR CIRCUIT Filed Aug. 28, 1945 March 2, 1 954 58 as 62 2 L 1"I I 34 54 44 V SOURCE or v NEGATIVE 1 6 GATE 36 40 -56 3o 5 I 52 2s 64 wv" f 46 II V ll 48 g LOAD 8mm! mm INVENTOR GEORGE R. GAMERTSFELDER QL L MW ATTORNEY Patented Mar. 2, 1954 UNITED STATES PATENT OFFICE 2,671,173 SHOCK EXCITED OSCILLATOR CIRCUIT George R. Gamertsfelder, Watertown, Mass. Application August 28, 1945, Serial No. 613,148

electron tube circuits, oscillator circuits of stable frequency.

, The primary object of the invention is to generally improve circuits of the character described. 5 A more particular object of the invention is to improve the circuit disclosed in a co-pending application of Edward F. MacNichol, Jr., Serial No. 617,137 filed September 18, 1945, Patent No. 2,638,548, granted May 12, 1953. In the circuit of the aforesaid application the tank circuit of the oscillator is connected in the cathode lead of a switch tube, so that one side of the tank circuit is connected to the cathode of the switch tube, whilethe other side of the tank circuit is connected to ground. The cathode heater is grounded in conventional fashion, so that the capacitance between the cathode and the cathode heater shunts the tank circuit. When it becomes necessary to replace the switch tube the new tube will ordinarily have a different heatercathode capacitance, and this in turn will change the resonant frequency of the tank circuit. Inasmuch as the circuitis being usedto generate a. train of oscillations for use as a marker for range finding purposes, it is important to avoid any such change in frequency. It is accordingly one object of the present invention to make the frequency of the tank circuit independent of the heater to cathode capacitance. To accomplish the foregoing objects and others which will hereafter appear, my invention resides in the circuit elements and their relation one to another as are hereafter more particue larly described, and sought to bedefined in the claims. The specification is accompanied by a drawing in which Figure 1 is a circuit diagram explanatory'of the operation of the invention; and Figure 2 shows voltage-time plots or wave forms explanatory of the operation of the circuit shown in Figure 1. Referring to the drawing, and moreparticularly to Figure 2,

8 Claims. (01. 25036) Referring now to Figure 1, the tank circuit is made up of an inductor l2 and a capacitor [4. This tank circuit is connected in the cathode lead of;a switch tube l 6 one side of the tank circuiti being connected to the cathode l8, and the other side being grounded at 20. It will be evident that-if the cathode heater 22 were connected to a grounded power supply, the capacitance between the cathode l8 and the cathode heater 22 would be connected in shunt across the tank circuit. Inasmuch as this capacitance is of appreciable magnitude relative to the capacitance l4, it would affect the frequency of the tank circuit, and replacement of the'switch tube 16 with another would shunt the tank circuit by a capacitance of different value, thereby changing the resonant frequency of the tank circuit.

In accordance with the present invention this difficulty is overcome by energizing the heater 22 by means of a separate transformer 24, the mid point of the secondary 26 of the transformer be ing connected by means of a lead 28 to a point in the circuit having substantially the same radio frequency potential as the cathode I8. More specifically the lead 28 is connected to the oath-- ode 30 of a cathode follower tube 32. Inasmuch as the gain in such a tube is substantially unity, the potential applied to the heater 22 is substantially the same as that existing on the cathode i 8. The capacitance of the heater transformer to ground is large, and may cause of the low impedance of a cathode follower circuit, there is no appreciable loss in thus shunt ing the heater circuit across the cathode circuit 64, including load 66 of the cathode follower tube 30, whereas a similar impedance loadconnected across the tank circuit would be undesirable.

. In the particular case here illustrated the ring ingtank circuit iz, I 4 has a tube acting as a negative resistance device to prevent decay of the oscillations. This idea broadly is not in itself new in the present invention, it being disclosed and claimed in the co-pending application of Edward F. MacNichol, Jr., referred to be called anoscillator, usual oscillators in having a limited amount of feed ack, which itself limits the amplitude of oscillation.

The oscillator comprises a pentode 31 having be variable, but be.1

its control electrode 36 coupled to the upper side of the tank circuit; its anode 38 connected to a B supply and thence to the lower and grounded side of the tank circuit, and its cathode 48 connected to an intermediate point on inductor l2. An adjustable series resistor 42 may be used to control the feed back, and thus to maintain the oscillations at constant amplitude, all as is described in the aforesaid co-pending application.

In the present case ithe control electrode '36 is connected through a coupling capacitor 44, and the bias on the grid is established by connecting it to an intermediate point between cathode resistors 46 and 48, by means of aseries ,gridresistor 50. This bias arrangement establishes the bias potential at a high enough value -to'permrt of equal potential swing in both directions, so that there will be no deformation of the desired sine wave form in the output. The tube operates class A, and a good sine wave shape is there- O z'for lobtained even :though the .output is znot taken irom the tank circuit, and instead is taken dimectly at the cathode "All. 1f the :outpnt were taken from the tank circuit, a change in the impedance of :the output circuit would change thexirequency of the tank circuit, or/and would change :the :feed back required. In the present case the output 'circuit'i'is dissociated from the tank circuit. Class .;A operation avoids loading the :tank circuit, and improves the frequency .sta-

bilitynndthewave fformzofithe output. The outiputzis cledr throughllead iz and coupling capacitor it :to :the .grid of *thccathode follower tube 32 previouslytreferredto.

"Izhe suppressor grid 58 :of rpentode .34 is .con-

nected to :the cathode. The screen :grid :is connected through capacitor '60 "to the cathode and therefore tis'at approximately the radio Ifrequency potential of the :controlgrid. The grid toscreen and 33,150 the grid "to cathode -.capacitances are thus minimized, and the tube 1'34 :may be changed without appreciably :afitecting "the frequency. Resistor 5,2 :is merely :a 'voltage dropping resistor.

It is believed that the construction and operation of my improved circuit, as well as the advantages thereof, will be apparent :from the :ioregoing detailed description. A negative gate :is applied to the :control electrode of the switch tube, thus removing the shunt current from the tank circuit, andstartingthe ringing of the .oscillator at full amplitude. On termination :of the negative ,gate the @oscillation is instantly damped out. The capacitance between the acathoderand the heater or the switch tube is without effect on the resonant frequency of the tank circuit,

because both are maintained at the same radio frequency potential. It is therefore possible to replace the switch tube with :another having a slightly different cathode to heater capacitance without shifting the frequency of the oscillator, and consequently without changing the accuracy of the marker wave applied to the oscilloscope.

.The wave form of the output is a good "sine wave. The oscillator tube as well as the switch tube may be changed without appreciable effect on .the marker ,irequency, because the screen grid connection minimizes the grid to screen and also the grid to cathode .capacitances. The tank circult is dissociated from the output load, so that the frequency stability .is not affected by changes in the output impedance. The classA operation of the oscillator tube provides a good sine wave output, even though the output is .not taken from the tank circuit.

While lnave shown and dose 'bedmy invention 4 in a preferred form, changes and modifications may be made without departing from the spirit of the invention, as sought to be defined in the following claims.

I claim:

1. A shock excited oscillator circuit for gen-- erating oscillations of stable frequency comprising a resonant loop, a cathode follower circuit, means to couple said resonant loop to said cathlode ifollower, zmeans including an .electron tube to excite said loop, said electron tube having a heater, a cathode, a control grid, and an anode, one side of said loop being grounded and the other .side zoi :sai'd :loop .being connected to said cathode, and a transformer having a tapped isolated 'secondary'winding for energizing said heater, said transformer tap being connected to the output of said cathode follower circuit at a point having substantially the same potential at the frequency of said oscillations as said cathode.

'2. A shock excited oscillator circuit ior gerierating oscillations :of .stable frequency and constant amplitude comprising a resonant loop, means for exciting said loop including an electron :tube having a heater, 1a -cathode, a control grid, and an anode, said loop being :in the-cathode ..circuit of said electron tube, an amplifier having input and output terminals, means -to couple said mputterminals to said loop, means to feed back to said loop energy iromsaid output terminals to supply the energy loss in said loop, acathode follower circuit, means to couple said output terminals to said cathode follower, an isolating transformer having .a tapped secondary winding for energizing said heater, said transtorm'er tap being connected to said cathode fol? lower circuit at a point having substantially the same potential .assaid cathode-at the frequency of said oscillations.

3. .A shock excited oscillator circuit for generating oscillations of stable frequency comprising a resonant loop, a cathode follower circuit, means to couple said cathode follower to said loop, means to excite said loop, said last means including .an electron tube having a heater, a cathode, a control grid and .an .anode, one side of said loop being grounded .and the other side of said loop being connected to said cathode, .a source of rectangular voltage pulses, .means for applying said pulses tosaid control grid to produce periodically discontinuous trains of oscillations 'in said resonant loop, and a transformer having a tapped isolated secondary winding ior. energizing said heater, said transformer tap being connected to sa'id cathode follower circuit at a pointihaving substantially the same potential as said cathode at the frequency of said oscillations.

4. A shock excited oscillator circuit 01 generating oscillations of stable frequency and constant amplitude comprising a resonant "loop, means for exciting saidloop, said means indluding an electron tube having a heater, a cathode, a. control grid, an anode, .said loop being in the cathode circuit of .said electron tube, a source of rectangular voltage pulses, means for applying said pulses to said control grid to produce ,periodically discontinuous trains of oscillations in said .resonant loop, a source of electrical energy, means connecting said heater to said source and means for maintaining said heater .at substantially the same potential as said cathode at the frequency of said -.os.cillations, tau amplifier having input and output terminals, means toacouple said input terminals to said loop, means to deed 5 back to said loop energy from said output terminals to supply the energy loss in said resonant loop, and an output load coupled to said output terminals.

5. A shock excited oscillator circuit for generating oscillations of stable frequency and constant amplitude comprising a resonant loop, means for exciting said loop, said means including an electron tube having a heater, a cathode, a control grid, and an anode, said loop being in the cathode circuit of said electron tube, a source of rectangular voltage pulses, means for applying said pulses to said control grid to produce periodically discontinuous trains of oscillations in said resonant loop, an amplifier having input and output terminals, means to couple said input terminals to said loop, means to feed back to said loop energy from said output terminals to supply energy loss in said loop, a cathode fol- I lower circuit, means to couple said output terminals to said cathode follower, an isolating transformer having a tapped secondary winding for energizing said heater, said transformer tap being connected to said cathode follower circuit at a point having substantially the same potential as said cathode of said electron tube at the frequency of said oscillations.

6. A circuit as defined in claim 5 in which said amplifier includes a pentode electron tube having screen grid and cathode connected through a capacitor in order to minimize the grid to screen and grid to cathode capacitances.

'7. A circuit as defined in claim 5 in which said amplifier includes a pentode electron tube having a control grid biased to permit class A operation and having screen grid and cathode connected through a capacitor in order to minimize the grid to screen and grid to cathode capacitances.

8. A shock excited oscillator circuit for producing oscillations of stable frequency, comprising a resonant loop, a source of power for energizing said loop, means for connecting said loop to said source, said means including a normally conducting electron tube having a control grid, an anode, a cathode and a heater, means for periodically biasing said electron tube to non-conduction to initiate oscillations in said loop, a cathode follower circuit, means to couple said resonant loop to said cathode follower, and a transformer having a tapped isolated secondary winding for energizing said heater, said transformer tap being connected to the output of said cathode follower circuit at a point having substantially the same potential at the frequency of said oscillations as said cathode of said electron tube.

GEORGE R. GAMERTSFELDER.

References Cited in the file of this patent UNITED STATES PATENTS Number Name Date 2,189,402 Pasma Feb. 6, 1940 2,273,193 Heising Feb. 17, 1942 2,386,844 Davis Oct. 16, 1945 2,403,725 Lawrence July 9, 1946 2,442,770 Kenyon June 8, 1948 2,443,619 Hopper June 22, 1948 

